Thread names on client-side : specific pool ?

Hi.

I have a service (webservice soap) sending rpc to a GRPC-server (spring-boot-grpc-starter).

When I look at the thread dump I see thread names like this : “grpc-default-worker-ELG-13-7”

or “grpc-default-executor-1”…

What are these threads ??

example of stack :

"grpc-default-executor-1" #972 daemon prio=5 os_prio=0 cpu=3938.33ms elapsed=306.27s tid=0x00007f410804a800 nid=0x431 waiting on condition  [0x00007f4049fde000]
   java.lang.Thread.State: TIMED_WAITING (parking)
	at jdk.internal.misc.Unsafe.park(java.base@11.0.3/Native Method)
	- parking to wait for  <0x00000000ea55fba0> (a java.util.concurrent.SynchronousQueue$TransferStack)
	at java.util.concurrent.locks.LockSupport.parkNanos(java.base@11.0.3/LockSupport.java:234)
	at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(java.base@11.0.3/SynchronousQueue.java:462)
	at java.util.concurrent.SynchronousQueue$TransferStack.transfer(java.base@11.0.3/SynchronousQueue.java:361)
	at java.util.concurrent.SynchronousQueue.poll(java.base@11.0.3/SynchronousQueue.java:937)
	at java.util.concurrent.ThreadPoolExecutor.getTask(java.base@11.0.3/ThreadPoolExecutor.java:1053)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.3/ThreadPoolExecutor.java:1114)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.3/ThreadPoolExecutor.java:628)
	at java.lang.Thread.run(java.base@11.0.3/Thread.java:834)

or

"grpc-default-worker-ELG-13-1" #940 daemon prio=5 os_prio=0 cpu=3135.01ms elapsed=345.67s tid=0x00007f40c0039800 nid=0x411 runnable  [0x00007f4046cad000]
   java.lang.Thread.State: RUNNABLE
	at sun.nio.ch.EPoll.wait(java.base@11.0.3/Native Method)
	at sun.nio.ch.EPollSelectorImpl.doSelect(java.base@11.0.3/EPollSelectorImpl.java:120)
	at sun.nio.ch.SelectorImpl.lockAndDoSelect(java.base@11.0.3/SelectorImpl.java:124)
	- locked <0x00000000ea568db0> (a io.netty.channel.nio.SelectedSelectionKeySet)

Epoll.wait ??? poll the grpcserver ? heartbeat ?

calls to the service itself are done by http thread like “http-nio-8080-exec-206”…On the other hand this one sounds logic because calls to the service are done synchronously.

[jvmlet]

https://groups.google.com/forum/m/#!forum/grpc-io

[chsi13]

Yes it is what I though that a special thread pool is used at client side … but I don’t know why because I see that calls on stub are made by http thread… btw calls are made synchronously … you proposed me to ask question to grpc-java project community ? Thanks for you answers